Speed regulation in motor controllers is often achieved by determining or measuring the speed of the motor and utilizing the speed in one ore more controller loops. For example, in some systems speed may be measured using a speed measuring sensor such as a tachometer. Speed sensors, or detectors of various types are well known in the art. In recent years the application of speed detection to motor control functions has stimulated demands on the sophistication of these sensors. In other systems, motor speed may be computed by evaluating the time rate of change of a position of the motor. In some systems motor speed may be estimated employing computational methodologies based on motor parameters and the like without employing a speed sensor.
One technique to estimate speed is known as sensorless commutation whereby a DSP (digital signal processor) or ASIC (application specific integrated circuit) integrates motor back-EMF of a non driven phase in a classic two-phase-on brushless DC (BLDC) system to derive an error signal. Unfortunately, such a system can only update (re-compute) a speed value during the neutral transition of each commutation state, at best. In PWM (pulse width modulated) systems, this signal is averaged over many commutation intervals which makes speed updates even less frequent.
Variation in motor speed is often undesirable and may be unacceptable is some systems. Speed regulation for a motor is achieved where speed is known or estimated with sufficient accuracy. FIG. 1 depicts an existing motor control system with motor speed feedback and direct current DC bus voltage feedforward. With this configuration for a controller, a speed variation must be resolved and then fed back to the a controller for the appropriate control corrections. Such corrections take time and as a result a speed deviation is experienced. It will also be appreciated that in such a system, where a (DC) bus supply compensation is employed, a disturbance resulting in a deviation of the voltage supplied to the motor is detected and feed to the controller for compensation to avoid a speed variations. As a result the motor speed is maintained as the DC bus voltage varies. It should be noted that some systems use multiple sensors, e.g., a sensor every n degrees, to acquire more frequent updates. However, feedforward bus sensing requires additional sensors to measure the DC bus voltage as well as sensors inputs to a controller for processing. Reduction of sensors and sensor inputs is always advantageous to save cost and limited space of a given implementation Therefore, a system and methodology for controlling motor speed more directly responsive to DC bus voltage is needed without DC bus voltage sensing.